1. Field of the Invention
This invention relates to internal combustion engines, and more particularly, to the fuel economy of internal combustion engines.
2. Description of the Prior Art
The recent emphasis on energy conservation has spawned interest in automotive transmissions. The prior art does recognize that an automative transmission can influence engine efficiency, and that this influence can be more important than the efficiency of the transmission itself. This is especially true in the case of a continuously variable ratio transmission, and the idea of using such a transmission to improve the operating efficiency of an associated engine is not new.
As an illustration, a given power level, say 15 h.p., can usually be produced throughout a broad range of crankshaft speed by adjusting the engine throttle to appropriately regulate the torque developed. However, peak efficiency for any particular power level will usually occur at only one distinct crankshaft speed. So if a fixed power level, 15 h.p. in this example, is required for 55 m.p.h. cruising or for climbing a hill at 30 m.p.h., or for any of the infinitely many speeds in between, then a continuous range of gear ratios must be available to permit the 15 h.p. to always be produced at the single most efficient crankshaft speed. This principle has been recognized.
What has not been recognized is that the design and calibration of the conventional automotive engine in large measure preclude really efficient operation. So while the prior art includes using a continuously variable ratio transmission to optimize the operation of the conventional automotive engine design, the inefficiency inherent in this design greatly limits the results. The relatively rich calibration of the conventional carburetor at w.o.t. (wide open throttle) best exemplifies this contradiction.
Using a conventional transmission, w.o.t. engine operation is not normally available for cruising, but rather is usually used only when maximum vehicle speed or acceleration is needed. Since a rich air-fuel ratio at w.o.t. does provide maximum engine torque, and thus maximum power at any particular crankshaft speed, the conventional carburetor calibration is in fact entirely appropriate when used in conjunction with a conventional automotive transmission. On the other hand, w.o.t. can be consistently available for even moderate cruising if a continuously variable ratio transmission is used. Since the extra power of a rich air-fuel ratio is gained at the expense of efficiency and is not needed for cruising, conventional carburetor calibration is entirely inappropriate for a continuously variable ratio transmission powertrain oriented toward fuel economy. Nevertheless, the great majority of prior art research and development work with the continuously variable ratio transmission automotive powertrain includes the use of w.o.t. air-fuel ratio enrichment, and this is but one example of the way in which the prior art has failed to consider the interrelationships of powertrain components. In the prior art related to continuously variable ratio transmission powertrains, emphasis has been on the transmission, but the engine is of at least equal importance.
In conclusion, the relatively high efficiency of the Otto thermodynamic cycle has been acknowledged. However, the idea that combustion variables can be optimized in the conventional Otto cycle automotive engine, and that a continuously variable ratio transmission is but one of the requirements for this optimization, is not within the prior art.